This invention relates to apparatus for driving a spindle of a machine tool, and more particularly apparatus for driving the spindle of the attachment exchange type wherein the construction of the apparatus is simplified.
In a machine tool, a working tool has been mounted on the spindle by holding the tool with a tool holder having a pull stud at its one end and by inserting the tool holder into a tool mounting opening formed at a free end of the spindle.
When the tool holder is inserted into the tool mounting opening of the spindle, the tool holder is clamped by a collet disposed in the spindle. Such clamping operation is effected by rearwardly pulling a drawbar mounted on one end of the collet for clamping the tool by dish shaped springs disposed in the spindle. Conversely, for dismounting the tool holder from the spindle the drawbar is moved against the resilient force of the dish shaped springs for disengaging the pull stud from the collet.
The spindle is rotated by a source of spindle drive installed in the machine tool, and the driving force is transmitted to the spindle through a bull gear fitted on the outer periphery of the spindle.
As above described, in the prior art spindle driving apparatus since a gear is fitted on the spindle as means for transmitting a torque to the spindle, it is necessary to arrange a gear meshing with the driving gear in parallel with the axis of the spindle with the result that the mechanism becomes large and complicated. Moreover, since the dish shaped springs are contained in the spindle, the outer diameter of the dish shaped springs must be small so that the number of laminated dish shaped springs would increase which increases the length of the spindle. Alternatively, the dish shaped springs may be positioned at the rear end of the spindle or at a position remote from the rear end. With the former construction there is a defect that the length of a portion to the rear of a gear train meshing with a gear fitted on the spindle increases. In any case, the length of a tool clamping drawbar inserted through the spindle increases.
Furthermore, where a driving apparatus contained in an attachment removably mounted on the ram of a machine tool is used as the driving apparatus of a machine tool, since the available space about the spindle of attachment is limited, the design of the gear device for driving the spindle of attachment becomes difficult and complicated. Since the axial length of the attachment is shortened, the disc shaped springs can be mounted on the upper end of the ram but the construction of the driving shaft in ram becomes complicated.